Color television picture tube screening method

ABSTRACT

The discontinuities on a correction lens having an effective surface made up of a plurality of elements are masked. The masked lens is displaced in a linear direction diagonal to the directions of the discontinuities during exposure of a picture tube screen. The diagonal corners of the mask pattern can be filled in to provide uniform exposure over the screen.

[ Jan. 1, 1974 3,628,850 12/1971 Yamazaki.............................95/1R 3,738,234

[ COLOR TELEVISION PICTURE TUBE 6/1973 Barten et al. 95/l R SCREENING METHOD Inventor:

F L t P rans' van Hekken ancas er a Primary ExaminerR|chard M. Sheen Attorney-Glenn H. Bruestle et al.

[73] Assignee: RCA Corporation, New York, NY.

May 2, 1973 Appl. No.: 356,455

22 Filed:

g an ef- 95/1R y of elements are I G031, 27/00 masked. The masked lens is displaced in a linear di- 95 rection diagonal to the directions of the discontinuities during exposure of a picture tube screen. The diagonal corners of the mask pattern can be filled in to provide uniform exposure over the screen.

[5|] Int. Cl.

[58] Field of References Cited UNITED STATES PATENTS 3,279,340 Ramberg et 95/1 R 14 Claims, 8 Drawing Figures ll o COLOR TELEVISION PICTURE TUBE SCREENING METHOD BACKGROUND OF THE INVENTION This invention relates to optical correcting lenses for use in laying down arrays of color phosphor deposits in cathode-ray tubes.

Many cathode-ray tubes have mosaic screens or targets of different light emitting or absorbing material. For example, certain types of color television picture tubes usually include a screen comprising arrays of red, green, and blue emitting phosphor lines or dots, electron gun means for exciting the screen, and a color selection electrode e.g., an apertured sheet metal mask or a wire grill, interposed between the gun means and the screen. In one prior art process for forming each color array of phosphor lines or dots on a viewing faceplate within a tube having an apertured mask, the inner surface of the faceplate is coated with a mixture of phosphor particles adapted to emit light of one of the three colors (e.g., green), and a photosensitive binder. Light is projected from a source through the apertured mask and onto the coating so that the apertured mask functions as a photographic master. The exposed coating is subsequently developed to produce phosphor elements of the first phosphor, e.g., green emitting lines or dots. The process is repeated for the blue-emitting phosphor and red-emitting phosphor utilizing the same apertured mask but repositioning the source of light for each exposure. A more complete description of a prior art process for forming a picture tube screen can be found in US. Pat. No. 2,625,734 issued to Law on Jan. 20, 1953.

In exposing the screen through themask apertures, the light source is sequentially placed in a fixed relationship with each center of deflection of each of the electron beams which later will excite the screen. Un-' fortunately, these deflection centers are not similarly fixed in position but rather vary in position during operation of the tube. One such variation is a shift toward the screen as theangle of deflection increases. This shift of the deflection center'parallel to the tube axis causes a radial misregister of the electron impingement spots on the screen with respect to their corresponding phosphor dots established using a fixed light source.

In the case of a dot screen where three beams are subjected to dynamic convergence, an additional type of deflection center shift occurs. This additional shift is traverse to the tube axis and causes degrouping (e.g., an increase in size of the electron spot trios) misregister of the electron spots related to their associated phosphor dots. These and other types of misregister are discussed in greater detail in the following U. S. Pat. Nos: 2,885,935 Epstein et al. and 3,282,691 Morrell et al.

In order to correct error between the position of electron beam landing and the location of a phosphor dot, the prior art has provided correcting lenses located between the light source and the tube screen which provide appropriate deflection of the light rays so as to locate the position of the phosphor dots at the expected landing positions on the screen of the electron beams. The design of correcting lenses for use in fabricating color television picture tubes has been described by Epstein et al in U. S. Pat. Nos. 2,817,276 and 2,885,935, by Ramberg in U. S. Pat. No. 3,279,340 and more recently by Yamazaki et al. in U. S. Pat. No.

3,628,850. The lenses disclosed in the latter two patents have discontinuous surfaces that permit more accurate exposure of the screen. However, because of the discontinuities in the lenses, reflection and light scattering occur at the discontinuous interfaces. Since reflection and scatter may cause misregister and uneven exposure, it isapparent that further development of screening methods utilizing correcting lenses with discontinuous surfaces is desirable.

SUMMARY OF THE INVENTION The present invention provides an improvement in a method of screening a color television picture tube. The basic method includes exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having discontinuities on an effective surface thereof. The improvement comprises masking the discontinuities and changing the relative position between the masked lens and the support in a linear direction diagonal to the directions of the discontinuities during exposure of the photosensitive material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partial plan view of a correcting lens having orthogonal discontinuities thereon;

FIG. 2 is a cross-sectional side view taken on line 2-2 of FIG. 1;

FIG. 3 is a partial plan view of a masked correcting lens;

FIG. 4 is a cross-sectional side view taken on line 4-4 of FIG. 3;

FIG. 5 is a cross-sectional side view of another masked correcting lens;

FIG. 6 is a partial plan view of yet another masked correcting lens;

FIG. 7 is a partial plan view of a masked correcting lens having rectangular elements; and

FIG. 8 is a partial plan view of a masked correcting lens having hexagonal elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. l and 2 depict a top plan view and a crosssectional side view, respectively, of a correction lens 10 for use in lighthouse screening of a color television picture tube. The lens has one surface 12 divided into a plurality of square elements 14. Each of these elements 14 provides a separate optical correction for screening a similarly shaped corresponding area of the tube screen. Because of this separate correction for each element, the slopes of adjacent elements may vary so that the interfaces between adjacent elements form discontinuities 16 and 18 in the lens surface 12. Since the elements 14 are square shaped and are aligned in rows in two directions, the discontinuities 16 and 18 are orthogonal to each other.

In using the lens 10 to screen a picture tube, the lens is placed between a light source and a tube faceplate that has been coated with a photosensitive material. Light is projected through the lens wherein its path is changed to the path an electron beam will take as it strikes the screen. However, a light striking the discontinuities l6 and 18 is deflected or scattered, thereby causing ambient defects on the screen.

To eliminate such unintended exposure, the discontinuities l6 and 18 are masked, as shown in FIG. 3 by a pattern of opaque stripes 20. Such masking can be accomplished in several ways, two of which are shown in FIGS. 4 and 5. The first masking scheme is incorporated in a lens package 26 depicted in FIG. 4. The package 26 includes the lens and a glass substrate 28 peripherally attached to the lens 10. The pattern of opaque stripes is attached to a surface of the glass substrate 28 so that each stripe of the pattern is directly opposite a surface discontinuity 16 of the lens 12. In an alternate masking scheme, shown in FIG. 5, opaque strips 20 are applied directly to the lens 10 over each of the discontinuities 16. Of course, other masking schemes may also be used for different lens constructions.

When the photosensitive material on a faceplate is exposed using a masked lens as shown in FIG. 3, an objectional pattern corresponding to the stripes l6 and 18 is formed on the screen. Therefore, to eliminate this objectional pattern, the position of the masked lens is changed in a linear direction, diagonally (45 angular degrees) to the two orthogonal directions of the discontinuities during exposure of the photosensitive material on the faceplate, as shown by lines 22 and 24 of FIG. 3. Although displacement of the lens in the diagonal direction will eliminate the shadow caused by the masking stripes, it is preferable to slowly oscillate the lens during screening a distance equal the diagonal distance between the intersections of adjacent discontinuities. Of course, this distance also equals the distance between centers of diagonally adjacent lens elements, as shown by line AA of FIG. 3. Ideally, to maintain relatively constant exposure, the velocity representation of such oscillation should approach a step function in contrast to the sinusoidal function of a free oscillator. Such step function is necessary to provide minimum dwell at the reversal points of the oscillation to ensure that the screen is evenly exposed and that the mask pattern does not appear on the completed screen.

When the lens is oscillated in the foregoing manner, nearly all light rays are intercepted twice by the diagonal width of two orthogonal mask stripes. The exception to this are the light rays intercepted at the intersection of two mask stripes which are only intercepted by the equivalent of the diagonal width of one mask stripe.

When the stripes are narrow, the difference in exposure between one and two stripe widths is essentially negligable. However, if, because of large fabrication tolerances, stripe width becomes large enough so that a diagonally overexposed pattern becomes apparent, the diagonal corners in the direction of displacement can be filled in with fillets 30 as shown in FIG. 6, of the same opaque material as the stripes 20. The diagonal distance across the mask between sides of the fillets should be equal to twice the diagonal width of a stripe so that the shadowing along each of the lines 22 and 24 are equivalent. Utilization of the fillets therefore permits even exposure over the entire screen when the masked lens is oscillated along line AA.

Of course, the present invention can also be applied to lenses with discontinuous surfaces other than square shaped elements. For example, the invention can also be applied to rectangularly shaped elements 38 and 40 as shown in the masked lens 32 in FIG. 7. In lens 32, the discontinuities 34 are masked by aligned opaque stripes 36. To effect even exposure over the entire screen, two corners of each lens element are masked by nonisosceles fillets 42 and-44 and the lens position is changed in a diagonal direction as indicated by lines 46 and 48 which are diagonals of elements 38 and 40, respectively.

FIG. 8 shows a masked lens 50 having hexagonal shaped elements 52 and 54. The discontinuities (e.g., 56, 58 and 60) are masked with opaque stripes (e.g., 62,64 and 66, respectively). However, in order to achieve uniform exposure the opaque stripes 62 extending in one direction are made wider than the other stripes 64 and 66. Therefore, when the lens 50 is moved perpendicular to the wide stripes 62 a distance equal to the distance between element center points or between parallel discontinuities, all parts of the screen will receive uniform exposure.

It can be seen from the foregoing embodiments that if lens movement and mask configuration are suitably selected, no pattern will appear on the tube screen since all portions of the screen will receive equal exposure. Of course, the constant speed and constant interference fraction described only provide uniform exposure if the light source intensity remains constant during exposure.

I claim:

1. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having discontinuities on an effective surface thereof, the improvement comprising,

masking the discontinuities and changing the relative position between the masked lens and the support in a linear direction diagonal to the directions of the discontinuities during exposure of the photosensitive material.

2. The method as defined in claim 1, wherein at least two of said discontinuities are orthogonal to each other.

3. The method as defined in claim 2, wherein the relative position between the masked lens and the support is changed by oscillating the lens in a linear direction substantially parallel to the effective surface of the lens.

4. The method as defined in claim 3, wherein the maximum peak to peak amplitude of the oscillations equal the diagonal distance between the intersections of adjacent discontinuities.

5. The method as defined in claim 2, wherein the relative position between the masked lens and the support is changed by oscillating the support in a linear direction substantially parallel to the effective surface of the lens.

6. The method as defined in claim 2, including masking the two opposite comers formed at an orthogonal discontinuity intersection that are located along the diagonal direction of displacement.

7. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having orthogonal discontinuities thereon, the improvement comprising,

masking the orthogonal discontinuities and two diagonally opposite corners formed at a discontinuity intersection,

oscillating the masked lens in the linear diagonal direction of the two diagonally opposite masked corners, the oscillations having a peak to peak amplitude equal to the diagonal distance between the intersections of adjacent discontinuities.

8. The method as defined in claim 7, wherein the velocity representation of the oscillations approaches a step function having minimal dwell time at reversal points of each oscillation.

9. The method as defined in claim 7, wherein the lens discontinuities are masked by applying an opaque material to a lens surface over the discontinuities.

10. The method as defined in claim 7, wherein the lens discontinuities are masked by an opaque pattern located on a transparent plate placed adjacent the lens.

lll. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having at least one discontinuity on an effective surface thereof, the improvement comprising,

masking said discontinuity with a masking component, said masking component being aligned with said discontinuity and said light source,

changing the position of the masked lens at a constant speed and a linear direction nonaligned with the elongated direction of said discontinuity to effeet uniform exposure of said photosensitive material.

12. The method as defined in claim 11, including a plurality of discontinuities on the lens effective surface forming hexagonal elements of said effective surface, each discontinuity being masked by a masking component.

13. The method as defined in claim 12, wherein masking components extending in one direction are wider than masking components extending in other directions and the position of said masked lens is changed in a direction perpendicular to the elongated direction of the wider masking component.

14. The method as defined in claim 11, wherein said effective surface has a plurality of orthogonal discontinuities and all discontinuities are masked with an opaque pattern shaped to provide uniform exposure of said photosensitive material as the position of said masked lens is changed a distance equal to a diagonal distance between discontinuity intersections.

Disclaimer 3,782,253.F1"ms Van H eklcen, Lancaster, Pa. COLOR TELEVISION PIC- TUBE TUBE SCREENING METHOD. Patent dated J an. 1, 1974. Disclaimer filed Mar. 26, 1976, by the assignee, BOA Oor'pomtion. Hereby enters this disclaimer to claims 1, 2, 3 and 5 of said patent.

[Oyfioz'al Gazette June 15, 1976.] 

1. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having discontinuities on an effective surface thereof, the improvement comprising, masking the discontinuities and changing the relative position between the masked lens and the support in a linear direction diagonal to the directions of the discontinuities during exposure of the photosensitive material.
 2. The method as defined in claim 1, wherein at least two of said discontinuities are orthogonal to each other.
 3. The method as defined in claim 2, wherein the relative position between the masked lens and the support is changed by oscillating the lens in a linear direction substantially parallel to the effective surface of the lens.
 4. The method as defined in claim 3, wherein the maximum peak to peak amplitude of the oscillations equal the diagonal distance between the intersections of adjacent discontinuities.
 5. The method as defined in claim 2, wherein the relative position between the masked lens and the support is changed by oscillating the support in a linear direction substantially parallel to the effective surface of the lens.
 6. The method as defined in claim 2, including masking the two opposite corners formed at an orthogonal discontinuity intersection that are located along the diagonal direction of displacement.
 7. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having orthogonal discontinuities thereon, the improvement comprising, masking the orthogonal discontinuities and two diagonally opposite corners formed at a discontinuity intersection, oscillating the masked lens in the linear diagonal direction of the two diagonally opposite masked corners, the oscillations having a peak to peak amplitude equal to the diagonal distance between the intersections of adjacent discontinuities.
 8. The method as defined in claim 7, wherein the velocity representation of the oscillations approaches a step function having minimal dwell time at reversal points of each oscillation.
 9. The method as defined in claim 7, wherein the lens discontinuities are masked by applying an opaque material to a lens surface over the discontinuities.
 10. The method as defined in claim 7, wherein the lens discontinuities are masked by an opaque pattern located on a transparent plate placed adjacent the lens.
 11. In a method of screening a color television picture tube by exposing a photosensitive material on a support with light emitted from a light source and passed through a lens having at least one discontinuity on an effective surface thereof, the improvement comprising, masking said discontinuity with a masking component, said masking component being aligned with said discontinuity and said light source, changing the position of the masked lens at a constant speed and a linear direction nonaligned with the elongated direction of said discontinuity to effect uniform exposure of said photosensitive material.
 12. The method as defined in claim 11, including a plurality of discontinuities on the lens effective surface forming hexagonal elements of said effective surface, each discontinuity being masked by a masking component.
 13. The method as defined in claim 12, wherein masking components extending in one direction are wider than masking components extending in other directions and the position of said masked lens is changed in a direction perpendicular to the elongated direction of the wider masking component.
 14. The method as defined in claim 11, wherein said effective surface has a plurality of orthogonal discontinuities and all discontinuities are masked with an opaque pattern shaped to provide uniform exposure of said photosensitive material as the position of said masked lens Is changed a distance equal to a diagonal distance between discontinuity intersections. 